Understanding the genetic and genomic basis of phenotypic traits is a major question in the biological sciences. One method to address this problem is the utilization of closely-related species that can be manipulated experimentally. The nematode Caenorhabditis elegans has long been a powerful tool for biological investigations and, as the first multicellular genome sequenced, has been an important point of reference for comparative genomics studies. However, this utility has been strongly limited to date by the fact that C. elegans has no known close relatives (i.e., with unsaturated non-coding positions) and that much of its natural biology of this organism remains a mystery. In the wild, Caenorhabditis nematodes proliferate on rotting fruit, and animals disperse to new sources of food via invertebrate carrier species. Recently, a new species of Caenorhabditis with exceptional characteristics, C. sp. 34, has been discovered. From a broader perspective, the most important feature of this species is that it is now the closest known relatives to C. elegans close enough to greatly advance comparative genomics. From a natural history perspective, this species has extremely interesting biology that can be immediately exploited using the power of the nematode system to gain deeper understanding behavioral and ecological genetics. For instance, this species is up to two times longer than C. elegans and are associated with fresh (not rotten) figs and fig wasps. My preliminary behavioral studies demonstrate that C. sp. 34 animals are attracted to fig wasps in the lab. Here, I propose to capitalize on the startling discovery and unique biology of these new species by characterizing the genomic features of C. sp. 34, by comparing these genomic characteristics with those of C. elegans and other Caenorhabditis species, and by investigating the genetic basis of phoretic-carrier chemoattraction in C. sp. 34. Genome assembly will be performed utilizing next-generation technology and modern computational methods. Additionally, comparative genomic approaches will be performed to understand the evolution of the genome architecture in Caenorhabditis. An ecologically-relevant experimental system to examine host-sensing in C. sp. 34 will be established with traditional chemotaxis assays. A forward mutagenesis screen will be performed in C. sp. 34 in order to identify mutants defective in sensing fig wasps in chemotaxis behavioral assays. The genome sequence will then mutation identification by direct sequencing in order to identify the molecular lesions responsible for host-finding defects. These genes will then be characterized using model systems genetic approaches. Results from these studies will provide insights into the genomic basis of novelty and improve genomic analysis of a critical biomedical model. Additionally, the genetic characterization of an unstudied behavior will improve our understanding of the evolution and development of the nervous system, and may reveal novel pathways that are functionally conserved across metazoans, including humans.